un ‧ sus ‧ tain ‧ a ‧ ble AC /ˌʌnsəˈsteɪnəb ə l/ BrE AmE adjective
[ Word Family: noun : ↑ sustenance , ↑ sustainability ; verb : ↑ sustain ; adjective : ↑ sustainable ≠ ↑ unsustainable ]
unable to continue at the same rate or in the same way:
unsustainable economic growth